High performance rapid prototyping system

ABSTRACT

A rapid prototyping system forms three-dimensional objects by depositing layers of material on a substrate. A planer stator containing a grid of stator elements is positioned above and generally parallel to the substrate. An extrusion head is magnetically suspended below the stator and is separated from the stator by an air bearing. An electromagnetic drive receives control signals from moving the extrusion head relative to the grid of stator elements. An umbilical provides mechanical damping to the head to reduce resonance of the head during movements.

BACKGROUND OF THE INVENTION

The present invention relates to the field of three-dimensionalprototype modeling. In particular, the present invention is a rapidprototyping system for forming three-dimensional objects ofpredetermined design by depositing multiple layers of a material in itsfluid state from an extrusion head onto a base. The material is selectedand its temperature is controlled so that it solidifies upon extrusionor dispensing onto the base, with the build-up of the multiple layersforming the desired object. In the present invention, the extrusion heador heads are driven by a linear motor and are attached to an umbilicalwhich provides mechanical damping to reduce resonance of the head duringmovements.

A rapid prototyping system involves the making of three-dimensionalobjects based upon design data which is provided from a computer aideddesign (CAD) system. Examples of apparatus and methods for rapidprototyping of three-dimensional objects by depositing layers ofsolidifying material are described in Crump U.S. Pat. No.5,121,329,Batchelder et al. U.S. Pat. No. 5,303,141, Crump U.S. Pat. No.5,340,433, Batchelder U.S. Pat. No. 5,402,351, Batchelder U.S. Pat. No.5,426,722, Crump et al. U.S. Pat. No. 5,503,785, and Abrams et al. U.S.Pat. No. 5,587,913, all of which are assigned to Stratasys, Inc.

Rapid prototyping allows the user to turn a design into a prototype totest form, fit, and function. There is a continuing need to producelarger parts through rapid prototyping. As the size of the parts beingproduced increases, higher speed movement of the extrusion heads andprecise control of extrusion head position is required.

SUMMARY OF THE INVENTION

The rapid prototyping system of the present invention deposits materialextruded by an extrusion head to build a three-dimensional object alayer at a time. The extrusion head is magnetically suspended below astator plate, and is separated from the plate by a fluid bearing. Drivesignals supplied to the extrusion head produce electromagnetic impulsesto move the head in x and y dimensions at high speed. An umbilicalconnected to the head provides mechanical damping which reducesresonance of the head during movements, so that the head position may becontrolled with high precision and reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exterior front elevation view of the preferred embodimentof the invention, showing the system in a build state.

FIG. 2 is an exterior elevation view of the right side of the preferredembodiment of the invention.

FIG. 3 is an exterior elevation view of the left side of the preferredembodiment of the invention.

FIG. 4 is a front elevation view of the prototyping envelope, showingthe system in a build state.

FIG. 5 is an electrical block diagram of the control system of thepreferred embodiment of the invention.

FIG. 6 is a partially exploded perspective view of the prototypingenvelope showing the modeling extrusion head in a build position.

FIG. 6A is a detailed view of a portion of FIG. 5 illustrating thevacuum platen grooves.

FIG. 6B is a detailed view of a portion of FIG. 5 illustrating the airbearing of the linear motor.

FIG. 7 is an exploded view of the filament spindle and filament spoolshown in FIGS. 2 and 3.

FIG. 7A is a perspective view of the outward face of the EEPROM board.

FIG. 8 is a front elevation of the modeling extrusion head, withportions shown in sectional.

FIG. 9 is an exploded view of the liquifier.

FIGS. 10A and 10B show an alternative embodiment of the liquifier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the preferred embodiment, the rapid prototyping system 10 iscontained within a cabinet 12, as shown in FIG. 1. The cabinet 12 hasdoors and covers located on a front, left and right sides thereof On thefront of cabinet 12, there is an envelope door 14, a modeling waste traydoor 16 to the right of envelope door 14, a touch screen display panel21 to the right of modeling waste tray door 16, a support waste traydoor 18 to the left of envelope door 14, and platform cover 20 belowenvelope door 14. A modeling drybox door 22 and an electronics bay cover24 are located on the right hand side of cabinet 12. A support dryboxdoor 26 is located above a compressor bay cover 28 on the left hand sideof cabinet 12.

The upper right hand side of cabinet 12 houses a modeling extrusionapparatus 30, which comprises a modeling extrusion head 32 attachedbelow a modeling x-y forcer 33 and connected to the end of a modelingarm 34 which rotates about a modeling pivot joint 36. Modeling extrusionapparatus 30 receives a filament of modeling material 40 from a modelingfilament spool 42 located in a modeling drybox 45 (FIG. 2) below pivotjoint 36 and accessible through modeling drybox door 22. Drybox 45maintains low humidity conditions to optimize the condition of filament40. Modeling extrusion apparatus 30 is used to dispense modelingmaterial in layers onto a substrate 60. Modeling filament spool 42mounted on a modeling spindle 43 in drybox 45 is more clearly shown inFIG. 2.

The left-hand side of cabinet 12 houses a support extrusion apparatus44, which is comprised of a support extrusion head 46 attached below asupport x-y forcer 52 and connected to the end of a support arm 48 whichrotates about a support pivot joint 50. Support extrusion apparatus 44receives a filament of support material 54 from a support filament spool56 located in a support filament drybox 57 (FIG. 3) beneath supportpivot joint 50 and accessible through support drybox door 26. Drybox 57maintains low humidity conditions to optimize the condition of filament54. Support extrusion apparatus 44 is used to dispense support materialin layers. Support filament spool 56 mounted on a support spindle 58 indrybox 57 is more clearly shown in FIG. 3.

Modeling material extruded in layers by modeling extrusion apparatus 30forms object 64. The support material is used to support anyover-hanging portions as the object is being built up. In building anobject, over-hanging segments or portions which are not directlysupported in the final geometry by the modeling material require asupport structure. Support filament 54 is supplied to support extrusionhead 46 which deposits material to provide the required support. Thesupport material, like the modeling material, is deposited in multiplelayers.

In building an object, only one extrusion apparatus at a time is in anactive, extruding state. In FIG. 1, the system 10 is shown building athree-dimensional object 64, with modeling extrusion apparatus 30 in anactive build state, and support extrusion apparatus 44 in a home restposition. When modeling extrusion apparatus 30 is in an active state,modeling filament 40 travels through arm 34 to extrusion head 32, whereis it heated to a liquid state. Layers of modeling material in a moltenstate are deposited by head 32 through a liquifier 59 protruding througha bottom surface of head 32, onto substrate 60. Substrate 60 issupported upon a vacuum platen 62 and held in place by vacuum forces.When support extrusion apparatus 44 is in an active build state, supporthead 46 similarly receives support filament 54 via arm 48, and heats itto a liquid state. Layers of support material in a molten state aredeposited by head 46 through a liquifier 65 protruding through a bottomsurface of head 32, onto substrate 60.

The filaments of modeling and support materials are each a solidmaterial which can be heated relatively rapidly above its solidificationtemperature, and which will very quickly solidify upon a small drop intemperature after being dispensed from the extrusion head. A compositionhaving a relatively high adhesion to itself upon which it is depositedwhen hot is selected for the modeling material. A composition having arelatively low adhesion to the model material upon which it is depositedis selected for the support material, so that the support material formsa weak, breakable bond with the modeling material and to itself. Whenthe object is complete, the support material is broken away by theoperator, leaving the object formed of modeling material intact.

The modeling material is preferably a thermoplastic material. Othermaterials that may be used for the modeling material filament includebees wax, casting wax, machinable and industrial waxes, paraffin, avariety of thermoplastic resins, metals and metal alloys. Suitablemetals include silver, gold, platinum, nickel, alloys of those metals,aluminum, copper, gold, lead, magnesium, steel, titanium, pewter,manganese and bronze. Glass, and particularly Corning glass would alsobe satisfactory. Chemical setting materials, including two-part epoxieswould also be suitable. A modeling material found to be particularlysuitable is an acrylonitrile-butadiene-styrene (ABS) composition. Amaterial found to be particularly suitable for the support material isan acrylonitrile-butadiene-styrene (ABS) composition with a polystyrenecopolymer added as a filler (up to about 80%) to create a lower surfaceenergy of the ABS composition, and to provide a lower cohesion andadhesion of the material. Both filaments of material are preferably of avery small diameter, on the order of 0.070 inch. The filament may,however, be as small as 0.001 inch in diameter.

FIG. 4 shows a build envelope 70 which is the central interior region ofthe system 10, accessible through envelope door 14. In FIG. 4, door 14,platform cover 20, and the adjoining face plates of cabinet 12 areremoved. The envelope 70 is where a three-dimensional object is built.Envelope 70 contains a build platform 74 which comprises vacuum platen62 supported by a set of legs 76, which ride on a platform drawer 78.Build platform 74 moves vertically in a z-direction within envelope 70.Movement of build platform 74 is controlled by a z-drive chain 80,driven by a z-motor 114 (shown schematically in FIG. 5). Build platform74 remains stationary during formation of a single layer. As eachadditional layer is deposited on substrate 60, build platform 74 islowered slightly so as to allow a space for forming the subsequentlayer. Platform drawer 78 pulls forward to allow the operator readyaccess to vacuum platen 62.

An electrical system 90, shown schematically in FIG. 5, controls thesystem 10. A CPU 92, together with first input/output (10) card 94 andsecond input/output (IO) card 96, control the overall operation of theelectrical system 90. CPU 92 receives instructions from the operatorthrough communication from touch screen display 21. Similarly, CPU 92communicates with touch screen display 21 to display messages for theoperator and to request input from the operator. CPU 92 in turncommunicates with 10 cards 94 and 96. A power supply 98 supplies powerto electrical system 90.

Envelope heaters 100 and envelope blower 102 establish and maintain atemperature in the envelope 70 of approximately 80° C. An envelopethermal cutout (THCO) switch 108 carries current through the machine'smain contractor actuation coil. If the temperature reaches approximately120° C. the THCO switch opens and current through the main contractor tothe system is interrupted. The head blowers 104 and 106 supply air atambient temperature to cool the pathway of filaments 40 and 54 as theytravel into modeling extrusion head 32 and support extrusion head 46,respectively.

CPU 92 also controls a compressor 110. Compressor 110 suppliescompressed air alternately to x-y forcers 33 and 52 provides a vacuum toplaten 62. CPU 92 provides layering drive signals to selectively actuatethe z-motor 114, which drives platform 74 along the z-axis.

Card 94, under the control of CPU 92, sends and receives signalsassociated with modeling extrusion head 32 and the filament supplythereto. IO card 94 sends drive signals that control the movement andposition of x-y forcer 33. IO card 94 further sends and receives signalsto and from modeling extrusion head 32, which includes a thermocouple222 (TC), a heater 220 (HTR), a motor 246 (MTR) and a safety switch 210(SS) (shown in FIGS. 8-10). Safety switch 210 shuts down the system ifthe temperature in the modeling extrusion head 32 gets too high.

IO card 94 monitors data concerning modeling material filament spool 42through communications with a modeling drybox processor board 116.Modeling drybox processor board 116 is mounted inside of modelingfilament drybox 45. It receives data concerning the modeling filamentfrom a modeling filament sensor 118 (located at the inlet to filamentguide 236, shown in FIG. 8) and a modeling EEPROM board 120, which is acircuit board carrying an electronically readable and writeable device(EEPROM 88, shown in FIG. 7)) attached to modeling material filamentspool 42. EEPROM board 120 acts as an electronic tag with a variety offunctions. It informs the control system 90 of the type of filament thatis on the spool and of the lineal feet of filament on the spool. Asfilament 40 is wound off of the spool 42, the CPU keeps track of howmuch material was commanded to be extruded, subtracts this amount fromthe total on the EEPROM 88 and writes the new value to the EEPROM 88drybox processor board 116 communicate with drybox processor board 116to update the data as to the amount of filament remaining on the spool42. Preferably, the data on EEPROM board 120 is encrypted so that it canbe updated the CPU 92. Filament sensor 118 senses and indicates thepresence or absence of filament at the entrance to the filament feedtube. With filament remaining on the spool, the operator can then grabahold of the filament and extract it from the extrusion head 32.Unloading of the used filament and spool and reloading of a new spool isthereby made easier.

CPU 92 receives the modeling filament data from IO card 94. At theoutset of a job, the CPU 92 will calculate whether a spool 42 or 56contains enough filament to complete the job. Operator notification isthen provided via touch screen display 21, stating either that thefilament is adequate to complete the job, or that the filament spoolwill need replacement and reloading during the process. Also at theoutset of a job, the CPU verifies that the modeling filament material onthe spool is the same material specified in object data. If thesematerials are not the same, an operator notification is provided viatouch screen display 21, providing the operator an opportunity to switchspools.

IO card 94 additionally monitors the temperature in the envelope 70 viasignals received from envelope thermocouple 122, and it sends signals toand from a modeling head proximity sensor 124, a high-z proximity sensor126, a low-z proximity sensor 128 and an xyz noncontact tip positionsensor 130, all of which are described below.

IO card 96 serves similar functions as IO card 94, for the supportextrusion head 52 and the filament supply thereto. IO card 96 sendsdrive signals that control the movement and position of x-y forcer 52.IO card 96 further sends and receives signals to and from supportextrusion head 46, which includes a thermocouple (TC), a heater (HTR), amotor (MTR) and a safety switch (SS). The safety switch SS shuts downthe system if the temperature in the modeling extrusion head 46 gets toohigh.

IO card 96 monitors data concerning support material filament spool 56through communications with a support drybox processor board 132. Itreceives data concerning the support filament from a support filamentsensor 134 and a support EEPROM board 136, attached to support materialfilament spool 56. EEPROM board 136 acts as an electronic tag, in thesame manner as EEPROM board 120. CPU 92 receives the support filamentdata from support processor board 132, and uses it to provide operatorinformation in the same manner as described above with respect to themodeling filament.

IO card 96 further controls a first pressure valve 138 and a secondpressure valve 140, which alternately open and shut to direct the flowof air from compressor 110. When valve 138 is closed and valve 140 isopen, air from compressor 110 is directed to modeling head x-y forcer33. When valve 138 is open and valve 140 is closed, air from compressor110 is directed to support head x-y forcer 52. IO card 96 in additioncommunicates with support head proximity sensor 142, which is describedbelow.

To create an object using rapid prototyping system 10, an operator mustfirst power up the system by pressing a power on switch (not shown),located on touch screen display 21. The system 10 then enters amaintenance mode, in which the system executes a routine to calibratethe locations of modeling extrusion head 32, support extrusion head 46,and build platform 74. The calibration is done in two phases. In thefirst phase, the system initializes movement boundaries for theextrusion heads and the platform. Modeling head proximity sensor 124initializes boundaries of the modeling head 32, and support headproximity sensor 142 initializes boundaries of the support head 44.High-z proximity sensor 126 and low-z proximity sensor 128 togetherinitialize the boundaries of platform 74. In the second stage, the xyznoncontact tip position sensor 130 initializes the position of the tipsof liquifiers 59 and 65. The xyz noncontact tip position sensor 130 is amagnetic sensor imbedded in platform 74 which detects position of theliquifier tips with three displacement degrees of freedom. Tip positionsensor 130 is of the type described in co-pending application Ser. No.08/556,583, which is incorporated by reference.

After calibration is complete, the system exits the maintenance mode andenters a standby state. In the standby state, the design of athree-dimensional object 64 is input to CPU 92 via a LAN networkconnection (shown schematically in FIG. 5) utilizing CAD software suchas QUICKSLICE® from Stratasys, Inc., which sections the object designinto multiple layers to provide multiple-layer data corresponding to theparticular shape of each separate layer. After the layering data isreceived, the system 10 enters a warmup phase, during which the envelope70 is heated. Upon reaching a temperature of 80° C., the system enters abuild state during which it creates the three-dimensional object.

The modeling extrusion apparatus 30 is shown more particularly in FIG.6. Modeling extrusion apparatus 30 is movable in a horizontal plane in xand y directions. Modeling x-y forcer 33 is positioned beneath andparallel to a planer stator 150, which contains a grid of statorelements (not shown). Together x-y forcer 33 and planer stator 150 forman electromagnetic linear stepper motor 152. Commercially availablelinear stepper motor, are available from Northern Magnetics, Inc. ofSanta Clarita, Calif. The x-y forcer 33 consists of two sets ofsingle-axis forcers mounted at 90° to each other and permanent magnetswhich hold forcer 33 against the stator (not shown). A compressed airsupply 154, supplied by compressor 110, is provided to x-y forcer 33when modeling apparatus 30 is active. The compressed air supply 154flows upward through x-y forcer 33 and exits through a top surfacethereof, as is illustrated in FIG. 6B. The exiting air forms an airbearing 156 between x-y forcer 33 and planer stator 150, which allowsnearly frictionless motion of the forcer in a horizontal plane belowplaner stator 150. Drive signals to x-y forcer 33 are received throughan electrical supply 158 which powers a stepper motor driver locatedwithin x-y forcer 33 (not shown) to achieve motion. Ordinarily, linearstepper motors of this type exhibit abrupt jarring motions which createmechanical resonance. This resonance typically precludes use of suchmotors in high-precision systems such as rapid prototyping systems. Asdescribed below, an umbilical to the head creates the surprising resultof providing a damping effect sufficient to allow high-precisiondeposition at speeds far exceeding those possible in prior art rapidprototyping systems.

Modeling extrusion arm 34 is a flexible chain carrier that is flexiblein a horizontal plane and substantially rigid in other directions. Arm34 carries within it air supply 154 and forcer electrical supply 158.Arm 34 also carries within it a modeling extrusion head electricalsupply 160 and a flexible air tube 162 which contains an ambient airsupply and modeling filament 40, as depicted in FIG. 8. Arm 34 togetherwith air supply 154, forcer electrical supply 158, extrusion headelectrical supply 160 and air tube 162 containing filament 40 form anumbilical 163 to extrusion head 32. The umbilical 163 creates thesurprising result of damping the mechanical resonance of extrusion head32 with respect to stator 30, which is produce by acceleration anddeceleration of the head 32 by forcer 33. In the preferred embodiment,the combined weight of head 32 and x-y forcer 33 is less than or equalto approximately 8 lbs.

The resonant frequency is about 55 Hz for small oscillations and about45 Hz for large oscillations, and the damping time to achieve 98% of thefinal value (which is equal to approximately 4 times the damping timeconstant) in this embodiment is less than or equal to about 150 ms.Oscillation and damping of mechanical resonance may be expressed as:A=A₀ sin (ωt+φ)e^(-t/)τ, where A=amplitude, A₀ =initial undampedamplitude, w=2πf=resonant frequency of the system, φ=a phase constant,t=time, and τ=damping time constant. Critical damping occurs when τ=1/ω.In the preferred embodiment described, the system is approximately afactor often from being critically damped. Further damping can,therefore, be added if desired. The damping time constant is affected bythe combined weight of extrusion head 32 and x-y forcer 33. The lighterthe weight, the shorter the damping time constant.

Damping of mechanical resonance is achieved primarily by frictionalforces produced during movement of umbilical 163. Alternatively, otherforms of damping means can be used, such as an oscillation dissipater(or shock-absorber) carried in extrusion head 32. Also, further dampingcan be produced by decreasing the resistivity of the bucking of starter150 (such as by using copper rather than steel) to increase eddy currentlosses within stator 150.

While FIG. 5 has been described as depicting modeling apparatus 30, itshould be understood that support head apparatus 44 has a similarstructure and has an umbilical of the same type described with referenceto modeling apparatus 30. Specifically, support x-y forcer 52 shares theplaner stator 150 such that x-y forcer 52 and stator 150 form a secondlinear motor. Support apparatus 44 starts from the opposite side ofcabinet 12 from modeling apparatus 30. For ease of reference, only onehead is shown in detail.

Vacuum platen 62 and substrate 60 are shown in an exploded fashion inFIG. 6. Vacuum platen 62 has a top surface 167 comprised of a grid ofgrooves 164, shown in detail in FIG. 6A. In the preferred embodiment,grooves 164 are 0.06 inches deep, 0.06 inches wide, and are 1 inch oncenter apart. An orifice 166 extends through the center of vacuum platen62. Orifice 166 receives a vacuum hose 168 which connects to vacuum pump112. When the system 10 is powered up, a vacuum is applied to vacuumplaten 62 by vacuum hose 168 and vacuum pump 112. The vacuum provided toplaten 62 pulls air through grooves 164 to distribute the vacuum alongthe platen. This vacuum holds the substrate 60 against the top surface167 of platen 62. In the preferred embodiment, substrate 60 is aflexible sheet. A polymeric material forms a suitable flexible sheetsubstrate. An acrylic sheet with a thickness of about 0.06 inches hasbeen successfully used as a substrate. When a desired object is formed,the operator can remove substrate 60 from the platen 62 by lifting onecorner of the sheet and breaking the seal of the applied vacuum.

Flexible substrate 60 can be flexed away from the object to peel thesubstrate from the object, if there is a weak breakable bond betweensubstrate 60 and the object. This weak, breakable bond may be formed bydepositing a first layer (or layers) of modeling material followed by asecond layer (or layers) of support material on the substrate 60. Themodeling material and substrate are selected so that the modelingmaterial is fully adhesive to the substrate. In forming an object, themodeling material is deposited in one or more layers on the substrate60. The support material is then deposited in one or more layers overthe modeling material. The object is then built up on the supportmaterial, using a plurality of layers of modeling and/or supportmaterial. When the object is complete, vacuum is broken by lifting acorner of the substrate 60, and the substrate 60 is removed from theplaten 62 by the operator. By flexing the substrate 60, the operatorthen peels the substrate 60 from the object. The first layer(s) ofmodeling material will remain adhered to the substrate, but the weakbond between the first layer(s) of modeling material and the secondlayer(s) of support material is a readily separable joint which breaksto allow removal of the substrate 60 without damage to the object.

Other flexible sheet materials may be used as substrate 60. For example,plain or coated paper, metal foil and other polymeric materials aresuitable. For high temperature support and modeling materials, apolymeric material (e.g., Kapton) or metal foil is particularlydesirable.

Although a vacuum is a preferred way to achieve a releasable hold downforce to hold substrate 60 against platen 62, other means for providinga releasable hold down force can also be used. For example, substrate 60can be held against platen 62 by an electrostatic chuck or by a weaklyadhering adhesive applied to the bottom surface of the substrate 60 orthe top surface of the platen 62 (or both).

FIG. 7 shows a detailed exploded view of the filament spool and spindleshown in FIGS. 2 and 3. The mechanical configuration of the filamentspool and spindle is identical for both the modeling filament and thesupport filament. For convenience of reference, FIG. 7 is directedspecifically to modeling filament spool 42 and modeling spindle 43.Spindle 43 extends horizontally from drybox 45 and has a semi-circularshape. A semi-circular connector 174 having a set of six depressibleconnector pins 176 is mounted on top of spindle 43 adjoining drybox 45.A spring-loaded latch 178 is embedded in the top of spindle 43 at anouter edge 179.

Filament spool 42 is comprised of a center barrel 180 on which filamentmay be wound, a pair of spool flanges 181 extending from either end ofbarrel 180, a sleeve 182 that fits within barrel 180 for receivingspindle 43, and modeling EEPROM board 120 mounted inside sleeve 182 andperpendicular to barrel 180. Barrel 180 rotates about sleeve 182 so thatfilament 40 may be unwound from spool 42. Sleeve 182 has a flange 184 atone end, a flange 186 at the opposite end, and an interior semi-circularcavity for receiving spindle 43. In the preferred embodiment, flange 184is removable and flange 186 is fixed. Removal of flange 184 allowswithdrawal of sleeve 182 from barrel 180. As mentioned above, EEPROMboard 120 carries EEPROM 188. In a preferred embodiment, EEPROM board120 is mounted adjacent fixed flange 186 by a pair of screws 190, sothat EEPROM 188 faces inward towards sleeve 182 for protection. EEPROMboard 120 on its outward facing side carries a set of six roundelectrical contacts 192, as shown in FIG. 7A. Connectors 192 areconfigured so as to provide a receiving surface for connector pins 176when spool 42 is mounted on spindle 43.

Latch 178 must be manually depressed to allow insertion or removal ofspindle 43 from sleeve 182. When sleeve 182 is mounted on spindle 43,latch 179 rests in an upward position so as to lock spool 42 into placesuch that contacts 192 fully depress connector pins 176. When filamentspool 42 is manually inserted onto spool holder 43, electrical contactbetween EEPROM board 120 and drybox processor board 116 is made throughthe connector 190.

Detail of the extrusion apparatus is shown in FIG. 8. While FIG. 8 showsmodeling extrusion apparatus 30, it should be understood that supportextrusion apparatus 44 contains the same parts and operates in the samemanner as modeling extrusion apparatus 30, at a 180° rotation. Extrusionhead 32 is mounted below x-y forcer 38 by a pair of mounting plates 200.Two pairs of bolts 202 attach head 32 to plates 200. Two bolts 204connect plates 200 to x-y forcer 38 to hold head 32.

Extrusion head 32 is formed of a inclosure 206 which holds liquifier 59,a filament drive 208 and safety switch 210. Liquifier 59 comprises athermal conducting thin-wall tube 212, a heating block 214, an extrusiontip 216, a tip retainer 218, heater 220 and thermocouple 222. FIG. 9shows liquifier 59 in an exploded view. As shown in FIG. 9, thin-walltube 212 has an inlet end 224, and is bent at a 90° angle. In thepreferred embodiment, tip 216 is soldered into the outlet end of tube212. Alternatively, a nozzle 226 may be brazed or welded to tube 212 inplace of tip 216. Using a 0.070 inch filament, tube 212 preferably hasan inner diameter of about 0.074 inches. The wall thickness of tube 212is preferably between 0.005-0.015 inches. It is desirable to keep tube212 as thin as possible to achieve maximum heat transfer across tube 212to filament 40. Other metals may also be used, such as brass, copper,tungsten, titanium, molybdenum, beryllium copper or other steels. Otherthermal conducting materials such as polymide (Kapton), a plastic with ahigh melting temperature, may also be used to form the thin-wall tube.

Tube 212 fits into a channel 229 of heating block 214, between a frontsection 228 and a rear section 230 of the heating block. Heating block214 is made of a heat conductive material such as aluminum or berylliumcopper. A set of four bolts 232 extend through outer section 228 andrear section 230 of heating block 214 to hold tube 212. When mounted inheating block 214, a first section of tube 212 adjacent the inlet end224 is exterior to heating block 214, and a second mid-section of tube212 is clamped within heating block 214, and a third section of tube 212including Tip 216 extends through the bottom of block 214. The firstsection of tube 212 forms a cap zone for the liquifier 59, the secondsection of tube 212 forms a heating zone, and the third section forms anozzle zone. The nozzle zone is contained within and silver soldered toextrusion tip 216, which is supported against heating block 214 by tipretainer 218, a square plate having a center orifice. Tip retainer 218is press fit around the extrusion tip 216, and mounted beneath heatingblock 214 by a pair of screws 234.

The length of the cap zone of tube 212 is in the range of 0.15 inchesand 2 inches. The cap zone must undergo a temperature gradient fromabout 70 degrees C. envelope temperature to about 280 degrees C.liquifier temperature. A shorter cap zone allows for greater control bythe system over the rate that molten filament is extruded (i.e., flowrate), but makes it more difficult to maintain a cool temperature forthe filament through the cap zone. The length of the heating zone isanywhere from 0.04 inches to 7 inches. The longer the heating zone, thehigher the maximum extruded flow rate, but the slower that the flow ratecan be accelerated and decelerated. A liquifier having a cap zone ofbetween 0.02-0.04 inches long and a heating zone of about 2.5 incheslong has been successfully used in a preferred embodiment of the system.

Cylindrical heater 220 and thermocouple 222 extend horizontally intorear section 230 of heating block 214. Heater 220 is positioned in heatexchange relation to the heating zone of tube 212, to heat the tube to atemperature just above the melting temperature of the filament. Using anABS composition for the filament 40, the tube is heated to about 270degrees C. Thermocouple 222 is positioned adjacent tube 212 to monitorthe temperature in the tube. Safety switch 210 will cause the system 10to shut down if temperature exceeds a predetermined level.

A guide tube 236 guides filament 40 from pivot 36 to extrusion head 32,made of a suitable low friction material such as Teflon for support inmotion. As described above, filament 40 within guide tube 36 are locatedwithin flexible tube 60 contained inside of arm 34. Filament 40 entersextrusion head 32 through an inlet aperture 238. Inside of extrusionhead 32, filament 40 is fed through a tapered guide 240 having arestricted guide passage 242. Filament drive 208, comprised of a steppermotor 246, a pully 248 and a pair of feed rollers 250 and 252. Roller250 has a drive shaft 254 which is driven by stepper motor 246. Roller252 is a rubber-coated idler. Filament 40 is fed from the guide passage242 of tapered guide 240 into a nip between rollers 250 and 252. Therotation of roller 250 advances filament 40 towards liquifier 59. Theinlet end 224 of thin-wall tube 212 is positioned to receive filament 40as it passes through rollers 250 and 252. The flow rate of the moltenfilament out of liquifier 59 is controlled by the speed at whichfilament drive 208 advances the filament 40 into liquifier 59.

A blower 256 blows air at ambient temperature into flexible tube 60 tocool guide tube 236 and filament 40. Cooling of strand 40 is importantso as to maintain the filament at a sufficiently low temperature that isdoes not become limp and buckled within the passages leading into theliquifier 59. Air from blower 256 travels through tube 60 and entersextrusion head 32 via an air conduit 258. Air conduit 258 provides apath for the air which is in a forward and parallel position fromfilament 40 within extrusion head 32.

FIGS. 10A and 10B show an alternative embodiment of the liquifier. FIG.10A shows liquifier 259 in an assembled view, while 10B shows liquifier259 in an exploded view. In this embodiment, two thin-wall tubes 260Aand 260B of the type described above flow into one, nozzle 262. Aliquifier of this type can be substituted into the dispensing head shownin FIG. 8 to provide one extrusion head that dispenses, at alternatetimes, two different deposition materials. The two deposition materialsmay be a modeling and a supply material, or they may be modelingmaterials of two different colors or having other diverse properties.Nozzle 262 is brazed or welded to the outlet ends 264 of tubes 260A and260B. Nozzle 262 is positioned in a vertical orientation, while tubes260A and 260B may be angled towards the horizontal. Separate feedmechanisms (not shown) are provided for tubes 260A and 260B so thatfilament material is fed into only one of the tubes at any given time.

Thin-wall tubes 260A and 260B are held into position by a heating block266. Heating block 266 is comprised of an outer plate 268, an interiorplate 270 and a rear plate 272. Rear plate 272 is mounted within theextrusion head, and holds a heater 274 which extends between tubes 260.Two channels 276 which hold tubes 260A and 260B are routed throughinterior block 270. A set of five bolts (not shown) extend through outerplate 268, interior plate 270 and rear plate 272 to detachably holdtogether liquifier 259. It is an advantageous that the liquifier beremovable from the heating block, for replacement and cleaning.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

We claim:
 1. A rapid prototyping system having a first extrusion headmovable in a first and second dimensions for depositing layers of afirst solidifying material in a desired pattern and a control forcontrolling operation of the system, comprising:first electromagneticlinear motor for driving the first extrusion head in response to drivesignals received from the control; and first damping means for dampingmechanical resonance of the first extrusion head during movements. 2.The rapid prototyping system of claim 1 wherein:the first damping meansis an umbilical extending from the extrusion head to a pivot joint, thedamping means being flexible along a horizontal plane and substantiallyrigid in other directions.
 3. The rapid prototyping system of claim 2wherein:the umbilical provides a path for a filament of first material,electrical signals to the first extrusion head, electrical signals tothe linear motor, and an air supply to the linear motor.
 4. The rapidprototyping system of claim 1 wherein:the first damping means has adamping time constant of less than or equal to approximately 150milliseconds.
 5. The rapid prototyping system of claim 1 and furthercomprising:a second extrusion head movable in the first and seconddimensions for depositing layers of a second solidifying material in adesired pattern; a second electromagnetic linear motor for driving thesecond extrusion head in response to drive signals received from thecontrol; and second damping means for damping resonance of the secondextrusion head during movements.
 6. The rapid prototyping system ofclaim 5 wherein:the second damping means is an umbilical extending fromthe extrusion head to a pivot joint, the damping means being flexiblealong a horizontal plane and substantially rigid in other directions. 7.The rapid prototyping system of claim 6 wherein:the umbilical provides apath for a filament of second material, electrical signals to the secondextrusion head, electrical signals to the second linear motor, and anair supply to the second linear motor.
 8. The rapid prototyping systemof claim 5 wherein:the second damping means has a damping time constantof less than or equal to approximately 150 miliseconds.
 9. A rapidprototyping system comprising:a substrate; a planar stator positionedadjacent and generally parallel to the substrate, the stator containinga grid of stator elements; an extrusion head positioned adjacent andmovable parallel to the stator, the extrusion head having an extrusiontip facing the substrate from which material in a molten state can beextruded for deposition onto the substrate; and an electromagneticforcer for moving the extrusion head relative to the grid of statorelements in the stator in response to drive signals received from acontrol and having an fluid bearing upper surface; and damping means fordamping mechanical resonance of the head with respect to the stator,produced by acceleration and deceleration of the head by the forcer. 10.The rapid prototyping system of claim 9 wherein:the planar stator isposition in a horizontal plane and the extrusion head and the substrateare positioned below the planar stator.
 11. The rapid prototyping systemof claim 10 wherein:the control signals control movement of theextrusion head along x and y axes which lie in a horizontal plane. 12.The rapid prototyping system of claim 11 and further comprising:meansfor controlling movement of the substrate along a vertical z axis whichis orthogonal to the x and y axes.
 13. The rapid prototyping system ofclaim 12 and further comprising:means for supplying air under pressureto form an air bearing between the fluid bearing surface of theextrusion head and the stator.
 14. The rapid prototyping system of claim13 wherein:the damping means is an umbilical extending from theextrusion head to a pivot joint, the damping means being flexible alonga horizontal plane and substantially rigid in other directions.
 15. Therapid prototyping system of claim 14 wherein:the damping means has adamping time constant of less than or equal to approximately 150milliseconds.